Finishing a BMS raw forging

gnxtc2

Well-Known Member
Staff member
Sending out my raw forging to have it finished. Going with a 3.625 stroke. Should I go with wide or narrow journal (don't have the rods yet)? I understand the BMS cranks are internal balance. Any other specs I should tell them to do?

If I go with wide journal, who makes bearings for the wide journal rods?

Thanks

Billy T.
gnxtc2@aol.com
 
Billy,

I have a couple of forgings and I had contemplated the same thing. I'd tell you if it was me I'd have it machined as a narrow journal crank. This is only because you can find a lot of used rods that are wide journal (typically On center) which you can buy for a good deal and narrow accordingly to suit your application. A narrow journal crank is actually stronger but you do lose some bearing surface area.

Neal

gnxtc2 said:
Sending out my raw forging to have it finished. Going with a 3.625 stroke. Should I go with wide or narrow journal (don't have the rods yet)? I understand the BMS cranks are internal balance. Any other specs I should tell them to do?

If I go with wide journal, who makes bearings for the wide journal rods?

Thanks

Billy T.
gnxtc2@aol.com
 
Marty,

A few years ago I had 5 Crower billet cranks that they had been mistakenly ground with BBC rod journals rather than Buick rod journals. One is in Len Freeman's Stage II engine and 1 is in Jeff Rands TA motor. Both guys used a 6.300" rod with a .927" pin dia. Jason Cramer is sitting on the one I sold to him and Nick Micale has the other 2. I have 2 BMS cranks that have SBC rod journal on them myself.

Neal

jjvites said:
Thats an interesting idea, anyone done this and which length of rod did you use?
 
jjvites said:
Thats an interesting idea, anyone done this and which length of rod did you use?

Rod length has to do more with expected use. For buicks it seems most try to fit the longest rod that they can into them; only draw backs to this is that the piston pins end up in the oil rings and your are forced to use 1/16 thick rings. This is not a problem if the engine is strictly a race motor. If the engine is going to see more street use ...my personal feeling is that I would use a shorter rod and get the pin location lower in the piston. This allows for the use of 3/16 rings and the piston pin location ends up more towards the middle of the piston (more stable and less likely to rock) I would just make sure that the rod lenght I used would give no less than 1.75 rod ratio.

As for crankshaft pin journal diameters...

I believe that Bill Anderson and Weber racing have/are offering eagle cranks that have been offset ground to sbc rod journals. Not sure how much stroke they were able to add. A turned steel crank is nothing to be scared of ... heck nascar engines currently use a rod journal size of 1.88 inches.

Whatever you end up deciding to do will require some special work on the bearings. As for the crank I have .030/.040. as Neal said in another thread that wide journal bearing would be hard to find... but they are not impossible. Numerous manufacturers will make them. I personally was planning to use just a standard narrow journal bearing ...which can be purchased from any discount chain auto parts store. The difference in width between a wide journal and narrow journal bearing is rather small.
 
chevyII said:
Or go to chevy journals and BB rods

Why?

If the crank was damaged then go with the Chevy route. This is a new crank. The Buick journals are bigger (should be stronger).

What size should the oiling holes be?

Neal, I bought the raw forging from you about 4-5 years ago. :biggrin:

Billy T.
gnxtc2@aol.com
 
straycat990 said:
I believe that Bill Anderson and Weber racing have/are offering eagle cranks that have been offset ground to sbc rod journals. Not sure how much stroke they were able to add. A turned steel crank is nothing to be scared of ... heck nascar engines currently use a rod journal size of 1.88 inches.

Ya but Nascar Chevy cranks dont have offset rod journal,Cutting the offset buick down that far has definelty got to weaken it.
 
KLHAMMETT said:
Ya but Nascar Chevy cranks dont have offset rod journal,Cutting the offset buick down that far has definelty got to weaken it.

I was not suggesting or implying that a buick even fire crank should be turned to 1.88 inches. I was just trying to show that over time engine builders have discovered that a smaller journal have more benefit than a larger size journal. Chevy nascar builders use to use a 2.100 journal and now use a 1.88. That is a sizable reduction in size. Some of the benefits for using smaller size journals is that the bearing speed is reduced, less oil required to feed the bearing, and less friction. Which all adds up to more HP.
 
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